An LED consists of a semiconductor junction, which emits light due to a current flowing through the junction. At first sight, it would seem that LEDs should be able to make an excellent replacement for the traditional tungsten filament incandescent bulb. At equal power, they give far more light output than do incandescent bulbs, or, what is the same thing, they use much less power for equal light; and their operational life is orders of magnitude larger, namely, 10-100 thousand hours vs. 1-2 thousand hours.
However, LEDs have a number of drawbacks that have prevented them, so far, from being widely adopted as incandescent replacements. Among the chief of these is that, although LEDs require substantially less power for a given light output than do incandescent bulbs, it still takes many watts to generate adequate light for illumination. Whereas the tungsten filament in an incandescent bulb operates at a temperature of approximately 3000° (degrees) K, an LED, being a semiconductor, cannot be allowed to get hotter than approximately 120° C. The LED thus has a substantial heat problem: If operated in vacuum like an incandescent, or even in air, it would rapidly get too hot and fail. This has limited available LED bulbs to very low power (i.e., less than approximately 3W), producing insufficient illumination for incandescent replacements.
One possible solution to this problem is to use a large metallic heat sink, attached to the LEDs. This heat sink would then extend out away from the bulb, removing the heat from the LEDs. This solution is undesirable, and in fact has not been tried, because of the common perception that customers will not use a bulb that is shaped radically differently from the traditionally shaped incandescent bulb; and also from the consideration that the heat sink may make it impossible for the bulb to fit in to pre-existing fixtures.
This invention has the object of developing a light emitting apparatus utilizing light emitting diodes (LEDs), such that the above-described primary problem is effectively solved. It aims at providing a replacement bulb for incandescent lighting having a plurality of LEDs with a light output equal in intensity to that of an incandescent bulb, and whose dissipated power may be effectively removed from the LEDs in such a way that their maximum rated temperature is not exceeded. The apparatus includes a bulb-shaped shell, preferably formed of a plastic such as polycarbonate. The shell may be transparent, or may contain materials dispersed in it to disperse the light, making it appear not to have point sources of light, and may also contain materials dispersed in it to change the bluish color of the LED light to more yellowish color, more closely resembling the light from normal incandescent bulbs.